Modern mobile devices are now often configured to utilize multiple subscriptions associated with various communication technologies for providing voice and/or data services to users. A multiple subscription mobile device may include a subscriber identification module (i.e., SIM or SIM card) for each subscription (or radio frequency chain) to enable data exchanges with different access networks. For example, the mobile device may use one subscription with a SIM card for a first carrier's access network and a second subscription with a second SIM card for a second access network. Multiple subscription devices may be especially useful in limiting roaming and long distance call fees (e.g., one subscription for Country A, another for Country B) and in differentiating services offered (e.g., one subscription for business use, another subscription for personal use, one subscription for data, another subscription for voice, etc.).
Some devices may be configured to operate as Dual Subscription, Dual Standby (or DSDS) mobile devices that may use a single radio frequency along with two SIMs and two modem stacks. DSDS devices may be enabled to transmit/receive a single voice call on a first SIM at a time, but may also exchange data on a second SIM concurrently. However, DSDS devices often suffer from degraded data throughput due to tune-away operations for monitoring and/or decoding data (e.g., pages), as well as the limitation of missing voice calls directed to a subscription when another subscription is being used for a voice call.
On the other hand, Dual Subscription, Dual Active (or DSDA) mobile devices may be configured to employ two or more transmit/receive (Tx/Rx) chains and transceivers to simultaneously exchange voice and/or data with different access networks and/or accounts. In other words, DSDA mobile devices may allow multiple SIMs (or SIM cards) to be active at the same time and may be connected to multiple networks at the same time. For example, a DSDA mobile device may initiate an active phone call on a first network, place the call on a local hold, and initiate another active phone call on the second network. DSDA mobile devices may switch between two calls without dropping either, enabling the receipt of a second call while maintaining a first call. DSDA mobile devices may have better performance than DSDS devices, as DSDA mobile devices may not experience tune away when on a data call since DSDA mobile devices have a second chain for monitoring pages. Further, DSDA mobile devices may receive call indications on a second subscription using the second chain when simultaneously on a voice call on a first subscription.
However, simultaneous communications in a DSDA mobile device may encounter coexistence issues that impact the performance of the mobile device. In particular, the transmit and/or receive chains of one subscription may encounter radio frequency coexistence issues, such as “desense” (i.e., radio interference that impacts the wireless link) based on the activity of the other subscription. For example, in certain band class combinations, the transmit (Tx) activity of one subscription may degrade the receive (Rx) operations on other subscriptions due to insufficient isolation in radio frequency hardware elements. Concurrently active subscriptions may also over-stress the processing capabilities of the mobile device (e.g., modem DSP processor overload), as well as other modules related to various signaling technologies (e.g., GPS and WLAN). For example, two active radio access technologies associated with subscriptions may not be able to support all their feature capabilities or max throughput due to insufficient horse power of a modem DSP processor. Additionally, concurrently active subscriptions may cause the mobile device to operate in violation of the amount of radio frequency radiation that can be emitted and absorbed in tissues of the user that are imposed by the Federal Communications Commission (FCC) (i.e., operate with unacceptable specific absorption rates or “SAR”). Power requirements inherent to DSDA functions may further drain the device battery (i.e., the device may operate with suboptimal battery current use and may require battery current limiting or “BCL”).
To avoid performance implications of such coexistence issues, the DSDA mobile device may need to perform various actions, such as Tx or RX blanking and firmware operation re-scheduling. However, determining the appropriate actions to take may require data from software that may slow otherwise fast firmware operations. Further, when a subscription in a DSDA mobile device has multi-mode capability, inter radio access technology concurrency issues may be experienced. Some existing techniques to assist DSDA mobile device performance may exist that use hardware and general purpose input/outputs to fire interrupts to notify radio access technology activities. However, these techniques may involve expensive, long operations that may include transmitting software information to logic components to analyze operating conditions (e.g., potential collisions/RAT interference, etc.) and then provide feedback to the software for further decision-making. For example, other techniques may involve numerous, synchronous acknowledgment signals (or ACK signals) between RAT software and a mobile device firmware in order to detect whether a coexistence scenario exists and determine how to handle it.